91 elements of the known 118 elements occur naturally on Earth. The other seventeen -- all elements beyond plutonium on the Periodic table, and three others -- technetium (43 electrons), promethium (61), and neptunium (93) -- are too unstable to exist on Earth and are not among the rare elements that are parts of the nuclear decay process of either thorium or uranium. The elements that do not occur naturally are synthetic. Synthetic elements are elements that have been created in a laboratory by artificial means. Synthetic elements are very unstable and have few commercial purposes. They decay into other elements in a fraction of a second. Most are created purely for research and experiment.

Synthetic elements are created in particle accelerators. Two smaller elements are accelerated to incredible speeds and collided into each other. Their nuclei merge together into a larger element. The element is studied by lab equipment before it decays.

Seven of the 91 naturally-occurring elements (polonium, astatine, radon, francium, radium, actinium, and protactinium) exist only in the presence of naturally-occurring radioactive elements uranium and thorium. These comprise all elements with atomic numbers 84 through 91 except for thorium (90). All isotopes of these elements are very short-lived, and those of them in use are used only for their radioactive properties (most notably in radium, and then as a desperate therapy for some cancers). Because of their short half-lives and the hazards associated with their radioactivity the chemistries of these elements are often extremely difficult to study.

Most synthetic elements have been named by the IUPAC, the international authority for naming chemicals. They are named after famous scientists or places where the elements were formed. For example, einsteinium (Es, 99) and americium (Am, 95). Some elements are too new to have official names. Before it can be named, an element must be discovered and proven to exist by a scientist or team. Then, the element's discoverer(s) will be allowed to choose a name. Until the element has a name, it is given a provisional name. Provisional names are made of a chain of words, each representing a digit in the element's atomic number. For example, ununseptium is element 117 , unnilpentium was element 105 (since renamed as dubnium), and unbioctium would be element 128 (not believed to exist).